The present invention relates to a method and apparatus for providing intelligent cellular handoff. In particular, the invention tracks a mobile station""s position with respect to a first base station and decides whether to hand off the mobile station to a second base station.
Wireless communication systems must provide service to many different geographical areas. Some of these areas are sparsely populated with wireless subscribers, such as suburban areas. Other areas are densely populated with wireless subscribers, such as urban areas. FIG. 1 shows these sparsely and densely populated areas and their associated cellular service topology. All areas are serviced with macrocells 12. The macrocells provide relatively high powered service to permit many subscribers to communicate with a public telephone network. Highly populated areas are additionally serviced with microcells 14. The microcells provide relatively low power service to permit large numbers of subscribers to communicate with the public telephone network.
The macrocells and the microcells coexist quite well. FIG. 2 shows the hardware connections that constitute the macrocells 12 and the microcells 14. The macrocells include macrocell base transceiver stations (MBTS) 18a-b that provide the transmission and reception of wireless communication. MBTS 18a-b are coupled to base station controller (BSC) 20. The microcells include base transceiver stations (BTS) 22a-c that provide transmission and reception of wireless communication. The BTS are coupled to BSC 24. Both BSC 20 and 24 are coupled to mobile switching center (MSC) 26, which is coupled to public switched telephone network (PSTN) 28.
When a mobile station (MS) 16 moves among the cells, the BSC and MSC control which particular cell communicates with the MS and which particular cell the MS is handed to when the MS moves from cell to cell. Ordinarily, this is not a problem. When the MS moves from a first cell to a second cell, the MSC instructs the BSC and BTS to communicate with the MS from the second BTS. However, when a MS moves rapidy from cell to cell, a large amount of communication control traffic occurs between the BTS, BSC and MSC. This occurs often, for example, when the MS is in a car driving through an urban area on a freeway. As a result, control communication between the BTS, BSC and MSC becomes excessive, which decreases the number of calls that the cellular network can handle.
Accordingly, a limitation of existing cellular network communications is that excessive control communication occurs when a MS moves rapidly among microcells. Additionally, a limitation of existing cellular technology is that a position of the MS cannot be accurately determined in order for the MS to be tracked and a trend of the position determined.
The invention relates to a method and apparatus for providing intelligent cellular handoff. In particular, the invention tracks a mobile station""s position with respect to a first base station and decides whether to hand off the mobile station to a second base station.
An exemplary embodiment of a cellular network according to the invention includes a receiver configured to receive inbound information from a mobile station. A correlator is coupled to the receiver and configured to correlate the inbound information against expected information to generate a correlator signal. An interpolator is coupled to the correlator and configured to interpolate the correlator signal to generate an interpolator signal. A memory is coupled to the interpolator and configured to store the interpolator signal. A processor is coupled to the memory and configured to process the interpolator signal to determine a position of the mobile station.
Additional embodiments track the position of the mobile station based on cellular hand off and mobile station position over time. The cellular network can transfer the mobile station from the microcellular network to the macrocellular network if the mobile station is moving rapidly. The cellular network can transfer the mobile station from the macrocellular network to the microcellular network if the mobile station is moving slowly.
Advantages of the invention include the ability to reduce control traffic among the network elements including the BTS, BSC and MSC. As a result, the inventive network can handle more telephone calls and can organize the calls more efficiently than in traditional cellular networks.